Field
Apparatuses and methods consistent with exemplary embodiments relate to a noise filter and an electronic device including the same, and more particularly to a two-stage noise filter and an electronic device including the same, in which two filters are integrated.
Description of Related Art
There are two kinds of noise, radiated noise and conducted noise. Radiated noise propagates through the atmosphere, and conducted noise propagates through a transmission line, such as a power line, a signal line, a ground line, etc., of an electronic device. Conducted noise is classified into common-mode noise C that propagates between the power line and the ground line, and normal-mode noise N that reciprocates between the power lines, as shown in FIG. 1.
Accordingly, a general electronic device includes a common-mode noise filter for filtering off the common-mode noise caused in the ground line, and a normal-mode noise filter for filtering off the normal-mode noise caused in the power line, thereby reducing electromagnetic interference (EMI) due to the noise.
In particular, the common-mode noise filter employs a one-stage noise filter or a two-stage noise filter where two one-stage noise filters are coupled, in accordance with mounted loads of the electronic device.
As shown in FIG. 2, the two-stage noise filter 1 is usually provided in a switching power supply (SPS) of the electronic device, and includes first and second filters 10 and 20, and a capacitor 30 arranged in between the first and second filters 10 and 20.
The first filter 10 includes first and second coils 11 and 13, and a first core 17 on which the first and second coils 11 and 13 are wound, and the second filter 20 includes third and fourth coils 21 and 23, and a second core 27 on which the third and fourth coils 21 and 23 are wound. The first to fourth coils 11, 13, 21 and 23 generate induced electromotive force based on variance in a supplied amount of electric current.
As shown in FIG. 3, the capacitor 30 is arranged in parallel between a connection line 15 of the first and third coils 11 and 21 and a connection line 25 of the second and fourth coils 13 and 23. The capacitor 30 serves to limit an electric current, which has a predetermined frequency and flows in between the first and third coils 11 and 21 and between the second and fourth coils 13 and 23, from exceeding a predetermined amount. First ends 11a and 13a of the first and second coils 11 and 13 are connected to power P. Second ends 21b and 23b of the third and fourth coils 21 and 23, which are opposite to first ends 21a and 23a, are connected to a load L via a rectifier or the like of the switching power supply (SPS).
Thus, when an alternating current (AC) having a predetermined frequency flows in between the first and third coils 11 and 21, and between the second and fourth coils 13 and 23, magnetic flux occurs in the first and second cores 17 and 27 by electromagnetic induction along arrows, as shown in FIG. 4. This magnetic flux suppresses the common-mode noise in the first and second cores 17 and 27.
However, such a conventional two-stage noise filter 1 increases the number of parts, the size and an occupied space because the first and second filters 10 and 20 are individually manufactured and respectively mounted on to a printed circuit board 30, thereby causing a complicated structure, increasing required man hours and raising manufacturing costs. Further, an electronic device with the conventional two-stage noise filter 1 has a limit to its miniaturization.